Is there any mechanism for observing that the whole container has "finished" painting?

[mmocny]

I understand that with Container Timing there are various issue that may make it impossible to know that a Container has fully finished painting:

• Some content may be below-the-fold, and user may scroll
• Some content may be offscreen, transparent, or obscured in ways that skip paint, but may move.

Etc.

But what about simple cases like: a container timing attribute applied to a single element leaf node (aka the element timing use case)?

Or for simple containers, where all potentially-contentful leaf nodes are known, and have all already reported contentful paints?